fix(ddtrace/tracer): ensure that sampling tests on remote config update are consistent

[darccio]

What does this PR do?

Modifies TestOnRemoteConfigUpdate to ensure that we replace the pattern below with equivalent require.Equal calls, as the test might pass without running some assertions.

if p, ok := s.context.trace.samplingPriority(); ok && p > 0 {
	require.Equal(t, samplerToDM(samplernames.RuleRate), s.context.trace.propagatingTags[keyDecisionMaker])
}

Reviewer's Checklist

• Changed code has unit tests for its functionality at or near 100% coverage.
• System-Tests covering this feature have been added and enabled with the va.b.c-dev version tag.
• There is a benchmark for any new code, or changes to existing code.
• If this interacts with the agent in a new way, a system test has been added.
• New code is free of linting errors. You can check this by running ./scripts/lint.sh locally.
• Add an appropriate team label so this PR gets put in the right place for the release notes.
• Non-trivial go.mod changes, e.g. adding new modules, are reviewed by @DataDog/dd-trace-go-guild.

Unsure? Have a question? Request a review!

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-11-21 13:58:23

Comparing candidate commit 8cbbc2d in PR branch push-rnqtmtwpyluy with baseline commit 81c9acd in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 15 metrics, 0 unstable metrics.

[datadog-datadog-prod-us1]

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 8cbbc2d | Docs | Datadog PR Page | Was this helpful? Give us feedback!}

[kakkoyun]

LGTM

[darccio]

/merge

[dd-devflow-routing-codex]

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2025-11-21 13:59:56 UTC ℹ️ Start processing command /merge

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2025-11-21 14:00:07 UTC ℹ️ MergeQueue: waiting for PR to be ready

This pull request is not mergeable according to GitHub. Common reasons include pending required checks, missing approvals, or merge conflicts — but it could also be blocked by other repository rules or settings.
It will be added to the queue as soon as checks pass and/or get approvals.
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---

2025-11-21 14:06:27 UTC ℹ️ MergeQueue: merge request added to the queue

The expected merge time in main is approximately 38m (p90).

---

2025-11-21 14:24:20 UTC ❌ MergeQueue: The checks failed on this merge request

Tests failed on this commit 43256fb:

• lint

What to do next?

• Investigate the failures and when ready, re-add your pull request to the queue!
• If your PR checks are green, try to rebase/merge. It might be because the CI run is a bit old.
• Any question, go check the FAQ.

[darccio]

/merge

[dd-devflow-routing-codex]

View all feedbacks in Devflow UI.

2025-11-21 14:27:16 UTC ℹ️ Start processing command /merge

---

2025-11-21 14:27:22 UTC ℹ️ MergeQueue: pull request added to the queue

The expected merge time in main is approximately 38m (p90).

---

2025-11-21 14:41:15 UTC ℹ️ MergeQueue: This merge request was merged